FOKKER-PLANCK DESCRIPTION OF PARTICLE CHARGING IN IONIZED-GASES

We present a Fokker-Planck description of the charging of particles we akly in ionized gases and of the charge fluctuations arising from the statistical nature of this process. Charge fluctuations constitute a M arkov process and in the limit of linear charging currents or large pa rticles this process is also Gaussian. The time scale of fluctuations is inversely proportional to the particle size and ion concentration a nd for small particles it is significantly larger than the particle di ffusion time. In this regime Brownian diffusion becomes a mechanism by which charge fluctuations are transported into different regions of t he plasma.